Since its discovery, the laser has resulted in many innovations and become a ubiquitous

The maser-the microwave progenitor of the optical laser-has been confined to relative obscurity owing to its reliance on cryogenic refrigeration and high-vacuum systems. Despite this, it has found application in deep-space communications and radio astronomy owing to its unparalleled performance as a low-noise amplifier and oscillator. The recent demonstration of a room-temperature solid-state maser that utilizes polarized electron populations within the triplet states of photo-excited pentacene molecules in a p-terphenyl host paves the way for a new class of maser. However, p-terphenyl has poor thermal and mechanical properties, and the decay rates of the triplet sublevel of pentacene mean that only pulsed maser operation has been observed in this system. Alternative materials are therefore required to achieve continuous emission: inorganic materials that contain spin defects, such as diamond and silicon carbide, have been proposed. Here we report a continuous-wave room-temperature maser oscillator using optically pumped nitrogen-vacancy defect centres in diamond. This demonstration highlights the potential of room-temperature solid-state masers for use in a new generation of microwave devices that could find application in medicine, security, sensing and quantum technologies.

This paper details the investigation of the quality factor (Q), dielectric permittivity (e r ) and temperature coefficient of resonant frequency (s f ) of the TE 01d mode of the columbite binary niobate ceramics, with the formula MNb 2 O 6 where M 5 21 cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 8001 to 14001C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M 5 Mn 21 , Co 21 , Ni 21 , Cu 21 , and Zn 21 , and the group II metal cations M 5 Mg 21 , Ca 21 , Sr 21 , and Ba 21 . All columbite niobates were found to have e r between 17 and 22 and negative s f values between -45 and -76 ppm/1C, and ZnNb 2 O 6 , MgNb 2 O 6 , CaNb 2 O 6 , and CoNb 2 O 6 had high Qf values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Qf of MgNb 2 O 6 was found to rise to over 95 000 GHz when heated at 13001C for 50 h. J ournal

Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation.